THE EXTINCT GENUS ERYMA. 341 
decapod Podophthalmia to which the Astacomorpha belong 
occurs in the Carboniferous formation. It is the genus 
Anthrapalemon—a small and very curious crustacean, 
about which nothing more need be said at present, as it 
does not appear to have special affinities with the Astaco- 
morpha. In the later formations, up to the top of the 
Trias, podophthalmatous Crustacea are very rare; and, 
unless the Triassic genus Pemphix is an exception, no 
Astacomorphs are known to occur in them. The speci- 
mens of Pemphix which I have examined are not suffi- 
ciently complete to enable me to express any opinion 
about them. 
The case is altered when we reach the Middle Lias. In 
fact this yields several forms of a genus, Hryma (fig. 80, B), 
which also occurs in the overlying strata almost up to the 
top of the Jurassic series, and presents so many variations 
that nearly forty different species have been recognised. 
Eryma is, in all respects, an Astacomorph, and so far as 
can be seen, it differs from the existing genera only 
in such respects as those in which they differ from 
one another. Thus it is quite certain that Astacomor- 
phous Crustacea have existed since a period so remote 
as the older part of the Mesozoic period; and any hesi- 
tation in admitting this singular persistency of type on 
the part of the crayfishes, is at once removed by the 
consideration of the fact that, along with Hryma, in the 
Middle Lias, prawn-like Crustacea, generically iden- 
tical with the existing Peneus, flourished in the sea 
